Coupled evolution of the stress concentration shell and fracture field during mining-induced overburden failure

Roof caving in longwall mining is governed by the coupled evolution of stress redistribution, fracture development, and load transfer in the overburden. However, the formation, migration, disruption, and reconstruction of the stress concentration shell during progressive roof failure remain insufficiently characterized. Taking the 1014 mining face of Yushuquan Coal Mine as the engineering background, this study developed an adaptive FLAC 3D -PFC 3D continuous-discontinuous framework in which the PFC 3D domain was dynamically updated according to the mining-induced plastic zone calculated by FLAC 3D . A damage-adjusted bonded-particle formulation represented progressive fracture development, and a physical similarity model with stress and AE monitoring provided trend-level validation. The numerical model reproduced seven roof caving events, with initial caving at 40 m and periodic intervals of 10–20 m. The stress concentration shell formed above the goaf, migrated upward and toward the advancing face, was disrupted during caving, and reconstructed after stress redistribution. The minimum stress in the unloading zone decreased to 3.1 MPa, whereas the front and rear arch-foot stresses reached 21.2 and 22.5 MPa, respectively. Force chain orientations shifted from predominantly vertical to inclined arch-like paths, providing a mesoscopic explanation for shell development. The proportion of fractures at 41°–60° and 121°–140° increased from 38.5 to 45.4% after initial caving and remained approximately 44.0% during large-scale collapse, consistent with increasing oblique fracture coalescence and bedding separation. The physical model reproduced the initial caving distance, comparable periodic caving intervals, and the overall stress concentration shell evolution. AE events concentrated near caving boundaries and damaged thick-hard roof strata, indicating spatial correspondence between active fracturing and stress concentration. These findings clarify the coupled stress-fracture mechanism governing overburden failure and identify stress concentration shell migration, and AE activity as potential indicators for critical monitoring regions and mining stages.